High-frequency signal translation circuit



Feb. 24, 1953 LA VERNE R. PHILPOTT 2,629,821

HIGH-FREQUENCY SIGNAL TRANSLATION CIRCUIT Filed June '7, 1945 5 LOW FREQ. OUTPUT RF. IN 22 ouTFu'r 2o;i owmv 35 T J as 3 LOCAL 9 OSClLLATOR 1, I 1: LOW I; FREQ. 3;! 53 OUTPUT D I Q 7 1 4 5 LF. OUTPUT 5m 15 LOCAL OSCILLATOR Qvwam fm LA VERNE R. PHILPOTT WWLWW Patented F eb. 24, 1953 UNITED STATES ATENT OFFICE HIGH-FREQUENCY SIGNAL TRANSLATION CIRCUIT (Granted under Title 36%;]. S. Code (1952),

11 Claims.

This invention relates to the transmission of a high frequency signal through a network comprising an electron tube, and is particularly directed to a method and means for doing so.

It is an object of the invention to transfer a high frequency signal by employing the electron transit time in a vacuum tube.

It is another object of this invention to provide a method and means by which the electron transit time in a vacuum tube is usefully employed to efiect detection or frequency conversion of high-frequency radio signals.

Another object of the invention is to provide a method and means for using conventional gridcontrol vacuum tubes for detection and frequency conversion of radio signals at frequencies higher than heretofore possible.

Still a further object of this invention is to provide a method and means for detection or frequency conversion of high frequency radio signals at very low electrical noise level, making possible high signal to noise ratio in receivers employing this invention.

This invention employs a vacuum tube with an external circuit so designed as to make use of the phenomenon of transit time. Transit time refers to the time required for an electron to travel between the electrodes of a vacuum tube. The magnitude of transit time in a given tube depends primarily on the element spacings and the tube voltages, which respectively govern the length of the path and the ele tron velocity.

In this invention, because transit time is taken into account and put to use, grid-control vacuum tubes of conventional structure may be operated successfully detectors or frequency converters at frequencies very much higher than with preexisting circuits. Moreover, due to the small voltages employed in this circuit, electron velocity is low and in consequence electrical circuit noise is very low, permitting high signal-tonoise ratio in hi h-frequency radio receivers employing the invention.

Further description of the invention will be i made with reference to the appended drawings of which,

Figure 1 is a cross-section view of a conventional tetrode vacuum tube, looking downward along the axis of the cathode;

Figure 2 is a schematic diagram showing an embodiment of the invention as a detector of high-frequency modulated signals;

Figure 3 is a schematic diagram showing an embodiment of the invention employing a pentode tube as a frequency converter for highfrequency radio signals;

Figure 4 is a schematic diagram showing a. form of the invention in which a tetrode tube is employed as a detector; and

Figure 5 is a schematic diagram showing a form of the invention in which a tetrode tube is employed as a frequency converter.

All the embodiments of the invention herein described employ electron transit time phenomena in vacuum tubes of conventional design. Figure 1 illustrates in cross-section the physical structure of a conventional tetrode tube that might be employed in this invention. The electrodes, enclosed within evacuated glass envelope 99, comprise cathode I00, anode Hi3, and grids lfll and H92, interposed concentrically between the cathodeand the anode,

Eifects caused by electron transit time limit the usefulness of such tubes in conventional circuits to frequencies wherein the period is very much longer than the transit time. In this invention that limitation is not present, and the upper useful frequency limit is greatly extended.

The form of the invention illustrated in Figure 2 is adapted to serve as a detector of modulated radio fre uency signals. In a specific construction in the form illustrated in Figure 2, circuit parameters were chosen to make the invention primarily responsive to amplitude modulated voltages.

The radio freouency signal voltage is brought in on coaxial line i, which is terminated in coupling loop 2. The currents in loop 2 induce radio frequency currents in the anti-resonant tank circuit consisting of inductive transmission line section 3 and tuning condenser 1. The radio frequency voltage developed at line terminal 5 is applied to grid [2 of vacuum tube 8, and the radio frequency voltage developed at line terminal 6 is applied to grid H of vacuum tube 8. Center tap a of line section 3 is connected to grid I ii of vacuum tube 8 and is also returned to cathode 9 of vacuum tube 8 through battery l8, which has negligible impedance to radio frequency currents. Cathode 9 is heated, and serves as an electron source. The heater element is not shown. Plate I3 of tube 8 is returned to cathode 9 through the load circuit consisting or resistor l4 and condenser l5 in parallel. Since plate 53 receives electrons from the cathode 9, it is hereinafter referred to as the anode. The magnitude of condenser I5 is so chosen that it possesses very low impedance to currents of the radio frequency, but high impedance to the modulation frequencies for which the radio frequency signal serves as carrier. Low frequency output terminals I6 and I! are connected across i to grid 2. electron velocity is so adjusted-as to make a halfterminated in coupling loop 22.

the load circuit comprising resistor I4 and condenser I5.

All three grids of tube 8 are at the same positive D. C. potential relative to cathode 9, thus potential being equal to the voltage of battery IS. The voltage of battery is is so adjusted that a substantial art of the electrons passing from cathode 9 to anode I3 require approximately half a radio frequency period to travel from grid II to grid I2. This voltage adiustment is not critical, and in a typical application the voltage of battery I8 may be 3 or 4 volts. The voltage on grid I is constant; this grid screens cathode 9 from grids II and I2 and influences the average electron velocity.

The radio frequency voltage applied to grid I2 should lag the radio frequency voltage ongrid I I by an amount of time approximately equal to the transit time of the electrons passing from grid In this particular embodiment the period of time the approximate lag. In consequence the input circuit isso connected that the voltage ongrid- I2 lags the voltage on grid l I by 180. Hence any electrons which are accelerated toward the anode by grid I I will be further acceleratedby grid I2, if their travel time from grid I to grid I2 is approximately half an R. F. period. This occurs because, after the electrons have passed grid II, the latter becomes negative and pushes the electronson towardgrid I2, whereas grid |2 at the same instant becomes positive and attracts them. After the said electrons pass grid |2, they are further accelerated toward the anode because sufficient additional time has by then elapsed. to cause rid l2 to become negative.

Electrons whose average velocity is of the-order specified cannot reach the anode if they approach grid I I at a time when it is negative, since they are repelled toward the-cathode by grid I Even if their kinetic energy is suflicient to carry them 'pastgrid' II while it is negative they then approach grid I2 a half-period later when it also is negative and the electrons are thus repelled from "the anode again. Such electrons either never reachthe anode or they moveabout in the elec- :tron cloud for a half-period of time andreturn when voltage conditions are favorable fortheir passage. As a'result the anode current of tube 8 contains impulses at the radio frequency. The effectiveness ofthe segregation or bunching process just described is a function of the amplitude of the radio frequency voltageapplied to grids I I and I2; and the anode current impulses are therefore of varyin magnitude if the R. F. signal voltage is amplitude modulated. Consequently the anode current of tube 8 contains components at the low modulation frequencies as well as the R. F. carrier frequencies. The load circuit, condenser and resistor I4, offer high impedance to these modulation frequencies, and accordingly modulation-frequency voltage is developed across output terminals IG and IT.

The embodiment of the invention shown in Figure 3 functions as a frequency converter for high frequency radio'signals. Radio frequency signal voltage is brought in on coaxial line 2|, The currents in loop 22 induce radio frequency currents in the anti-resonant tank circuit consisting of inductive transmission line section 23 and tuning condenser 21. The radio frequency voltage developed at line terminal 25 is applied to grid 32 of tube 28, and the radio frequency voltage developed at line --terminal 26 is-applied to grid 3| of tube 28. Gen- 4 ter tap 24 of line section 23 is returned to the cathode 29 of tube 28 through battery 20, which has negligible impedance to radio frequency currents. Grid 38 of tube 28 is connected to cathode 29 through radio-frequency choke coil 34. Grid 30 is also coupled to local oscillator 40 through condenser 39. The amplitude of the voltage impressed on grid 30 by local oscillator 40 may be controlled by varying the capacitance of Cathode 29 is heated and serves The heater element is not shown. The anode 33 of tube 28 is returned to cathode 29 through the load circuit consisting of inductance coil 35 and condenser 36 in parallel. The output terminals 31 and 38 are connected across the load circuit, coil 35 and condenser 36.

. Coil 35 and condenser 36 are so chosen that they will be anti-resonant at the desired intermediate output frequency. The frequency of local oscillater-4D is adjusted so that its frequency will bear a relation to the radio signal frequency such that the sum or difference of the signal frequency and the oscillator frequency will equal the desired intermediate output frequency. The amplitude of the voltage impressed on grid 30 by local oscillator 40 is set at a suitable value by adjusting condenser 39.

The operation of this frequency converter circuit is similar to that. of the detector circuit shown in Figure 2, with one important difference.

Whereas in the detector the average electron velocity is controlled by the grid-polarizing battery alone, in this circuit it is also dependent upon the instantaneous valueof the voltage impressed on-grid 30 by local oscillator). When the voltage on grid 30- is appreciably negative,

. anodeicurrent iscut off entirely. When grid 30 is positive, the average electron velocity is varied greatly as the potentialof grid 30 swings over a sired intermediate frequency. Since the load in the anode circuit, comprising coil 35 and condenser 36, is anti-resonant at the desired intermediate frequency, it will offer high impedance to current of that frequency and a voltage of that frequency will be developed across the output terminals 3'! and 38.

Figure 4 is a schematic diagram of another embodiment of the invention, connected as a detector of modulated ultra-high frequency radio signals, using in this case a tetrode vacuum tube. The vacuum tube 45 is shown in Figure 4 as containing cathode 46, grids 41 and 48, and anode 49. Cathode 46 is heated and serves as an electron source. The heater element is not shown. 45 is shown in Figure 4 as containing cathode 46, grids 41 and 48, and anode 49. Cathode 46 is heated and serves as an electron source. The heater element is not shown.

The radio frequency signal voltage is applied to coil 4|, and the resulting currents in coil 4| induce radio frequency currents in the antiresonant tank circuit'consisting of coil 42 and condenser 43 in parallel. "-Theradio' frequency voltage developed at tank circuit terminal 56 is applied to grid 48 of tube and the radio frequency voltage developed at tank circuit terminal 5! is applied to grid 41 of tube 45. Center tap 58 of coil 42 is connected to the cathode 46 of tube 45 through battery 44, which offers negligible impedance to radio frequency currents. Anode 49 of tube 45 is connected to cathode 46 through the load circuit comprising condenser 50 and. resistor 5| in parallel. A filter consisting of radio-frequency choke coil 52 and condenser 53 in series are connected across the anode load circuit, and low frequency output terminals 54 and 55 are connected respectively to the two sides of condenser 53. Condensers 5b and 53 are so chosen as to offer very low impedance to radio frequency currents but very high impedance to currents of modulation frequencies. Coil 52 is so chosen as to offer high impedance to radio frequency currents but low impedance to the modulation-frequency currents.

The voltage of battery 44 is set to such a value that a substantial fraction of the electrons moving from cathode to anode in tube 45 will require approximately half a radio-frequency period to travel from grid 41 to grid 48. This value of voltage is not critical in general, and if a standard miniature tube is used, will normally be three to four volts for frequencies of the order of lOOOrnc/s. For lower frequencies, less voltage is required.

Although grids 41 and 48 are at the same positive D. C. potential, their instantaneous potentials are free to vary with the oscillations in tank circuit 4243. The radio frequency voltage of grid 48, moreover. is 180 out of phase with the voltage on grid 41. Electrons approaching grid 41 when it is in the positive portion of its A. C. cycle will be accelerated by grid 41 more than will electrons approaching grid 41 during the negative part of its A. C. cycle. Hence for each cycle of A. C. voltage on grid 41 the electron stream beyond grid 41 will include a group of more-accelerated electrons outrunning the group of less-accelerated electrons. Since approximately half an R. F. period will have elapsed by the time the more accelerated grou reaches grid 48, the group finds grid 48 near its maximum positive potential also, and hence that group is accelerated again by a more-than-average amount. The less-accelerated group, arriving at grid 48 about a halfeiod later than the faster group, finds grid 48 in the negative portion of its A. C. cycle and hence near its least-positive potential. Consequently the slower group is again given less accelerative im etus than the first group of electrons, and the electrons reach the anode, not uniformly spaced. but in bunches, resulting in an anode current which contains A. C. components, of the radio frequency and of the modulation frequencies. The radio frequency components of the anode current are readily passed to the cathode by condenser 55, but condenser 50 and resistor 5| offer a high impedance to the modulation frequency components, and modulation frequency voltage is thus developed across resistor 5i. Any R. F. components of voltage across resistor 5! are filtered out by coil 52 and condenser 53, and voltage containing only modulation frequency components appears at output terminals 54 and 55.

The schematic diagram in Figure 5 illustrates an embodiment of the invention which uses a tetrode tube, in conjunction with lumped-constant circuit elements, as a frequency converter.

Vacuum tube 65 contains a cathode 61, grids and 69, and anode it. Cathode 61 is heated and serves as an electron source. The heater element is not shown.

The radio frequency signal voltage is applied to coil 6!, and the resulting currents in coil 6| induce radio frequency currents in the tank circuit comprising coil 64 and condenser 65 in parallel, which is anti-resonant at the signal frequency. Local oscillator 63 is connected to coil 52, which is also inductively coupled to tank circuit coil 64. Thus currents of the local oscillator frequency are also induced in the tank circuit 64, 65. Center tap '56 on coil 64 is connected to cathode 61 of tube 66 through battery 6i), which offers negligible impedance to radio frequency currents. Tank circuit terminal 14 is connected to grid 69 of tube 66, and the other tank circuit terminal 75 is connected to grid 68 of tube 65. Anode H! of tube 65 is returned to the cathode 61 through a load circuit comprising resistor ll, condenser i2, and inductance coil 13, all in parallel. Condenser l2 and coil 73 are antiresonant at the desired intermediate frequency. Resistor H is a damping resistor whose function is to broaden the frequency response characteristic of the anode load circuit. Output terminals l! and 18 are connected respectively to the anode if! and the cathode 61 of tube 66.

The coupling between coil 52 and coil 64 is adjusted until the peak voltage across coil 64 at the local oscillator frequency is several volts. The frequency of the local oscillator is so adjusted that the difference between the signal carrier frequency and the frequency of the local oscillator is equal to the desired intermediate frequency.

Like the other embodiments of the invention described in this specification, this circuit functions as a transit-time mixer. When. grid 68 is appreciably negative electrons cannot pass through it toward the anode. When grid 68 is positive, however, electrons are attracted to and through it; and during the portion of the cycle when the electron velocity is correct, grid 69 becomes positive at a sufficient time later to further accelerate toward the anode those electrons which have passed grid 68. The resulting pulses of electrons striking the anode produce A. C. components of anode current including a component at the desired intermediate frequency. This component of anode current encounters a high impedance in the anode load circuit. As a result a voltage of the desired intermediate frequency is developed across the anode load, and this voltage appears at output terminals Ti and 18.

It will be understood that the embodiments shown and described are exemplary only, and that the scope of the invention will be determined with reference to the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. A non-linear transmission circuit comprising an electron tube having at least anode, cathode and two grid electrodes, an output load circuit conductively connecting said cathode and anode electrodes to establish equal quiescent potentials thereat, a biasing means connected between said grids and said cathode applying a small positive potential to each of said grids to .7 .zproducea lowgaverageielectron velocity,--a source :of .high Q frequency signals having a :frequency whose half :period is substantially equal to 1 the electron transit time between saidgrids, an input circuitzcoupling'said high frequencysignals to said grids in oppositephase.

2..A non-linear transmission circuit comprising'an electrontube having at least-anode,oathodesanditwo-grid:electrodes, an output load'cir *cuit conductivel-y connecting said cathode and anodeelectrodes toestablish equal quiescent po- .tentialst-at said cathode and anode, a high. frequencyzsignalsource, an inputcircuit coupling saidsignalsourceto saidgrids in phase opposition, "awbiasingymeans connected between said,

jgrids-and' said' cathode applying a smallpositive potential to :each grid: to pro ducev a low average xelectron .velocity,-.and means'ior adjusting the 'potentiaLof-saidbiasing means to obtain anelec- :tron .transit time between saidgrids equal to a ;-half period of said signal.

1 3. A non-linear transmission circuitcomprisinglan electron tube having at least anode, cathode and two grid electrodes, an output load cir- "cuit conductively connecting said cathode and anode electrodes to-establish equal quiescent potentials at said cathodeand anode, a high frequency signal source, an input'circuit coupling said signal source'to said grids in phase opposition, a tap on said input circuit at a center point with'respect tosaidgrids, a-biasing means connected between said tap andsaid cathode applying a'small positive potential to-each grid to produce a low average electron velocity, and means for adjusting the potential of said biasing :means to obtain an electron transit time between said grids equal to a half period of said :signal'and'a' rectified signal at said anode.

4. A non-linear transmission circuit comprising'anelectron tube having at least anode, cathode and two grid electrodes, an output'load circuit conductively connecting said cathode and anode electrodes to establish equal quiescent-potentials'at said cathode and anode, a-high f1 quency signal source, a transformer having am 1- mary connected to-said signal source and a secondary with opposite ends connected respectively to said-gridelectrodes, a center tap on said secondary,'a biasing means connected-between said center tap and said cathode applying a small positive potential to each grid to produce a low-averageelectron'velocity, and vmeans for adjusting ithexpotent-ialof said biasing means to obtain an electron transit-time between said grids equal to :.a half periodof saidsignal and a rectified signal at saidanode.

5. A non-linear transmission circuit comprising an electron tubehavingg at least 'anode,.-'cathodeand two gridelectrodes,a source of modulated .high frequency signals, an input circuit tuned to said high frequency signals and coupling said signal source to said grids in phase opposition, a tapon said input circuit at a center point with respect to said'grids, a biasing means connected between said tap and said cathode applying a small positive potential to each grid to produce a low average electron velocity, an output load-circuit tuned to the modulationfrequency and conductively connecting said anode and cathode to establish equal quiescent potentials there- 'at, and means-for adjusting the potential of said biasing means'to obtain an'electron transit time betweensaid grids equal to a half period of said signal frequency and produceuthe modulation signal insaid outputcircuit.

'half' period of said 6. Anon-lineartransmission circuit compris- ,'ingan electron tube having atleast anode, cathode, and three grid electrodes, an output load circuit conductively connecting said cathode and anode electrodes to establish: equal quiescent potentials thereat, a biasing-means connected between said grids and said cathode applying a smallpositive.potential .to each of said grids to produce a low average electron velocity, a source of high frequencysignals having'a frequency whose 'halfperiod is substantially equal to the electron transit time betweenadjacent grids, an

input circuit couplingsaid high frequency signals to the two' grids more remote from said cathode, said signals-being coupled to the grids in opposite phase.

'7. A non-linear transmission-circuit comprising anlelectron tube havingat least-anode, cathode, and three grid electrodes, an output load circuit conductively connecting said cathode and anode electrodestto establish equal quiescent potentials at said cathode and anode,'a high'frequency signal source, an input circuit coupling said signal sourceto the two grids more remote fromsaid cathodes-aid signals being coupled to the grids in phase opposition, a biasing means connectedbetwcen grids and said cathode applying a small positivepotential to each grid to'produce a low-average electron velocity, and means foradjusting the potential of said biasing means to obtain an electron transit time between adjacent grids equal to a half period of said signal.

8. A non-linear transmission circuit comprising an electron tube having at least anode, cathode, and two grid electrodesyan output load circuit conducely connecting said cathode and anode electrodes 'to'establlsh equal quiescent potentialsthereat, a'biasing'nieans connected between said grids and said cathode applying a small positive potential to each of said grids to produce a low average electron velocity, a source of high frequency signals having a frequency whose half period is substantially equal to the electron transit time between said grids, an input circuit coupling said high frequency signals to said grids in opposite phase, and a local oscillator coupled to said grids.

A non-linear transmission circuit comprising an electron tube having at least anode, cathode, and two grid electrodes, an output load circuit conductively connecting said cathode and anode electrodes to establish equal quiescent potentials at said cathode and anode, a high frequency signal source, an input circuit coupling said signal source to said grids in phase opposition, a biasing means connected between said grids and said cathode applying a small positive potential to each'grid to produce a low average electron velocity, means for adjusting the potential of said bis ing means to obtain an electron transit time between said grids equal to a signals, and a local oscillator coupled to said grids.

18. A non-linear transmission circuit comprising an electron tube having at least anode, cathode, and three grid electrodes, an output load circuit concluctively'connecting said cathode and anode electrodes to establish equal quiescent potential'thereat, a biasing means connected be tween said cathode and'the two grids more remote therefrom applying a small positive potential to each of said remote grids to produce a low average'electron velocity, a source of high frequency signalshaving a frequency whose half period is substantially equal to the electron transit time between said remote grids, an input circuit coupling said high frequency signals to said remote grids in opposite phase, and a local oscillator coupled to the grid adjacent said cathode.

11. A non-linear transmission circuit comprising an electron tube having at least anode, cathode, and three grid electrodes, an output load circuit conductively connecting said cathode and anode electrodes to establish equal quiescent potentials at said cathode and anode, a high frequency signal source, an input circuit coupling said signal source to the two grids more remote from said cathode, said signal source being coupled to said remote grids in phase opposition, a biasing means connected between said remote grids and said cathode applying a small positive potential to each remote grid to produce a low average electron velocity, and means for adjustingthe potential of said biasing means to obtain an electron transit time between said remote grids equal to a half period of said signal, and a local oscillator coupled to the grid adjacent said cathode.

LA VERNE R. PI-l'ILPOTT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

